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Structural basis of Na+/K+-ATPase adaptation to marine environments

Nature Structural & Molecular Biology volume 14, pages 427–431 (2007)Cite this article

Abstract

Throughout evolution, enzymes have adapted to perform in different environments. The Na+/K+ pump, an enzyme crucial for maintaining ionic gradients across cell membranes, is strongly influenced by the ionic environment. In vertebrates, the pump sees much less external Na+ (100–160 mM) than it does in osmoconformers such as squid (450 mM), which live in seawater. If the extracellular architecture of the squid pump were identical to that of vertebrates, then at the resting potential, the pump's function would be severely compromised because the negative voltage would drive Na+ ions back to their binding sites, practically abolishing forward transport. Here we show that four amino acids that ring the external mouth of the ion translocation pathway are more positive in squid, thereby reducing the pump's sensitivity to external Na+ and explaining how it can perform optimally in the marine environment.

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Figure 1: Alignment of extracellular transmembrane helix linkers for different Na+/K+ pumps.
Figure 2: Charge moved during Na+ translocation by a heterologously expressed squid Na+/K+ pump.
Figure 3: Mutations in the outer surface of the squid Na+/K+ pump affect its affinity for Na+ ions.
Figure 4: Mutations in the outer surface of the squid Na+/K+ pump mapped on the crystal structure of the calcium pump.

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Acknowledgements

We thank P. De Weer, K. Swartz and S. Silberberg for useful discussions, the DNA sequencing facility at the NINDS, and P. De Weer, D. Gadsby, R. Rakowski and F. Bezanilla for participating in the experiment shown in Figure 3d. F. Bezanilla kindly provided software for the Innovative Integrations board. This work was partially supported by US National Science Foundation grant IBN-0344070, NIH grant NS039405-06, NIH National Center for Research Resources, Research Centers in Minority Institutions grant G12RR03051 and the Intramural Research Program of the NIH, NINDS.

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Authors and Affiliations

  1. Institute of Neurobiology, University of Puerto Rico-Medical Sciences Campus, San Juan, 00901, Puerto Rico, USA

    Claudia Colina & Joshua J C Rosenthal

  2. Structural Cell Biology Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke (NINDS), US National Institutes of Health (NIH), Bethesda, 20892, Maryland, USA

    Joseph A DeGiorgis

  3. Molecular Neurophysiology Unit, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke (NINDS), US National Institutes of Health (NIH), Bethesda, 20892, Maryland, USA

    Deepa Srikumar, Nikhila Iruku & Miguel Holmgren

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Correspondence to Joshua J C Rosenthal or Miguel Holmgren.

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Supplementary information

Supplementary Fig. 1

Amino acid sequence of squid Na+/K+ ATPase α subunit. (PDF 27 kb)

Supplementary Fig. 2

Amino acid sequence of squid Na+/K+ ATPase β subunit. (PDF 24 kb)

Supplementary Fig. 3

Quantification of α and β subunit mRNA in the giant axon system. (PDF 36 kb)

Supplementary Fig. 4

Functional expression of squid NsKα1 and NsKβ1 in Xenopus oocytes. (PDF 29 kb)

Supplementary Fig. 5

Enhancement of heterologous/endogenous expression ratio by making measurements exclusively in the oocyte's animal pole. (PDF 31 kb)

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Colina, C., Rosenthal, J., DeGiorgis, J. et al. Structural basis of Na+/K+-ATPase adaptation to marine environments. Nat Struct Mol Biol 14, 427–431 (2007). https://doi.org/10.1038/nsmb1237

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